LaRoche has been dealing with back problems for the entire road trip, but the pain grew worse in his final at-bat in the fifth inning against the Dodgers on Monday. LaRoche said he took muscle relaxers and the back feels "a little better." He was expected to spend most of Tuesday getting treatment.
"I don't know if that's temporary. … I would assume today is more treatment than actually going in and pushing it," LaRoche said.
During the current road trip, LaRoche is 1-for-23 and has seen his average drop to .257 for the season. He said the back problems had nothing to do with his recent slump.
"I felt it this whole road trip," LaRoche said. "The last two days was really the only time I felt it swinging. Before that, I felt it on defense, but I didn't feel it hitting [until recently]."
With LaRoche out, Kevin Frandsen received the start against Dodgers left-hander Clayton Kershaw.
Bill Ladson is a reporter for MLB.com and writes an MLBlog, All Nats All the time. He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.